Embodiments of the subject matter disclosed herein relate to washing systems, gas turbine engines, and methods of washing axial compressors.
Gas turbines are widely used as for power generators, for gas compression and in general for all the applications where it is required a rotating mechanical drive. A core element of a gas turbine engine is the compressor through which during operation huge quantity of air is drawn in and compressed. Burners add heat to the compressed air and the expanding combustion gases drive the turbine from which useful power can be extracted. The quality of air entering the compressor is a very important factor for the lifetime and the efficiency of the gas turbine. Such air contains various types of materials in form of aerosols like dirt and corrosive particles. Even if the majority of particles exits the gas turbine with the exhaust gases, a part of them can still deposit on the blades and vanes of the compressor especially on the front end where they eventually accumulate, deteriorating the aerodynamics and thus reducing the efficiency and the performances of the machine, resulting in great economic losses for the user. The flux of harmful particles leads also to other problems like FOD (Foreign Object Damage) and corrosion. For all these reasons measures have to be taken to control the quality of the air entering the gas turbine.
Normally the gas turbine inlet is equipped with air filters that block at least the particles having dimensions higher than a certain minimum. Still enough particles of smaller dimensions will be able to pass the filter system, adhering and accumulating on the blades and vanes of the compressor. This phenomenon, called “fouling”, makes necessary to resort to regular periodical washing of the gas turbine compressor to eliminate the deposits of these particles on the blades and vanes, trying in this way to recover the most of the compressor original performances. Washing the gas path of the compressor is normally accomplished by spraying washing fluids, through a series of nozzles that atomize such fluids, into the compressor intake and letting the rotor to rotate forcing the washing fluids through the compressor till they exit at the back of the machine. Normally, the washing operations are performed under two conditions, one so called “on-line” because the cleaning is done while the machine is operating, while the other washing method requires the machine to be off production and thus is called “off-line”.
The “on-line” washing is regarded as less effective than the “off-line”, because the machine is operating at full load and there are restrictions on the positions where to put the nozzles. In fact, due to the very high velocity of the air it is common to locate the nozzles in positions where the air stream has a low velocity and the washing liquid can penetrate into the center of the air flow otherwise due to the turbulence of the air flow and to the centrifugal force the washing liquid will move towards the periphery away from the blades. On top of this, high temperature tends to evaporate the washing liquids. An advantage of the “on-line” method is the fact that the machine can continue to operate.
The “off-line” methods require a momentary stop to the production since the machine in this case is only running with the starter at only a few percent of the normal full load speed. In the “off-line” washing normally the nozzles that spray the washing fluids are installed in front of the compressor low pressure first stage blades. In case of “off-line” washing, during washing operation the engine is rotating just to give to the washing fluids enough energy to scrape the foul without causing turbulence and without imparting to the fluid strong centrifugal forces that can push the fluid towards the compressor casing away from the blades to be washed. The choice of the particular positioning and assembling of the washing system is important for the washing efficiency and also for the gas turbine integrity.
According to a prior art solution, the spraying nozzles are installed inside the bellmouth of the gas turbine in a position such that the spray is directed straight at the compressor inlet in a direction almost parallel to the air flow. The disadvantage of this solution is that, in case of failure, the nozzles could cause damage to the gas turbine.
Another prior art solution, in case of machines with radial air inlet, consists in fixing the nozzles on the internal radial volute.
A drawback of both solutions is that the nozzles are inside the flow path within the machine with the possibility to create a flow distortion that will affect the performances of the machine.
Therefore, the necessity is felt of an improved washing system that can overcome the drawbacks.